Over the past few years, power systems (generation, transmission, and distribution) have undergone several major technological developments with optimized control as their ultimate aim. These developments rely on a better understanding of power system dynamics and inevitably require more instrumentation. In this context, it is important to minimize the electrical, mechanical and environmental impacts of new instrumentation, which must also meet particular reliability and precision requirements as well as isolation standards for each voltage level.
Generally speaking, current and voltage are the two primary inputs for all electrical parameter measurements. Measuring current is normally quite straightforward and meets the conditions mentioned above. Several sensors are available that do not even require an open circuit. In addition to a wide measurement range, excellent precision and a high degree of electrical isolation, these sensors are also robust and can be installed on a power system with no major service continuity impacts.
However, the same cannot be said of voltage measurement, which generally requires the use of measurement transformers connected in parallel with the line(s) forming the system. From a mechanical point of view, these voltage transformers are relatively heavy and their installation requires certain precautions. In addition, installing them on medium or high-voltage systems sometimes requires the use of a bypass disconnect switch so they can be isolated in case of malfunction.
A few years ago, measuring equipment suppliers started to develop voltage sensors that offer good precision with no galvanic contact. However, some of these sensors are quite large, and others require an external supply source.